The present invention relates to thienopyridine compounds which are potassium channel inhibitors. Pharmaceutical compositions comprising the compounds and their use in the treatment of arrhythmia, type-2 diabetes mellitus, immunological disorders, including rheumatoid arthritis, type-1 diabetes, inflammatory bowel disorder and demyelinating disorders such as multiple sclerosis are also provided.
Ion channels are proteins that span the lipid bilayer of the cell membrane and provide an aqueous pathway through which specific ions such as Na+, K+, Ca2+ and Cl− can pass (Herbert, 1998). Potassium channels represent the largest and most diverse sub-group of ion channels and they play a central role in regulating the membrane potential and controlling cellular excitability (Armstrong & Hille, 1998). Potassium channels have been categorized into gene families based on their amino acid sequence and their biophysical properties (for nomenclature see Gutman et al., 2003).
Compounds which modulate potassium channels have multiple therapeutic applications in several disease areas including cardiovascular, neuronal, auditory, renal, metabolic and cell proliferation (Shieh et al., 2000; Ford et al., 2002). More specifically potassium channels such as Kv4.3, Kir2.1, hERG, KCNQ1/minK, IKACh, IkAdo, KATP and Kv1.5 are involved in the repolarisation phase of the action potential in cardiac myocytes. These potassium channels subtypes have been associated with cardiovascular diseases and disorders including long QT syndrome, hypertrophy, ventricular fibrillation, and atrial fibrillation, all of which can cause cardiac failure and fatality (Marban, 2002).
The human delayed rectifier voltage gated potassium channel subunit, Kv1.5, is exclusively expressed in atrial myocytes and is believed to offer therapeutic opportunities for the management of atrial fibrillation for several different reasons (see review of Brendel and Peukert, 2002): (i) There is evidence that Kv1.5 underlies the cardiac ultrarapid delayed rectifier (Kv(ur)) physiological current in humans due to similar biophysical and pharmacological properties (Wang et al., 1993; and Fedida et al., 1993). This has been supported with antisense oligonucleotides to Kv1.5 which have been shown to reduce Kv(ur) amplitude in human atrial myocytes (Feng et al., 1997). (ii) electrophysiological recordings have demonstrated that Kv(ur) is selectively expressed in atrial myocytes, and therefore avoids inducing potentially fatal ventricular arrhythmia through interfering with ventricular repolarisation (Amos et al., 1996; Li et al., 1996; and Nattel, 2002). (iii) Inhibiting Kv(ur) in atrial fibrillation-type human atrial myocytes prolonged the action potential duration compared to normal healthy human atrial myocytes (Courtemanche et al., 1999). (iv) Prolonging the action potential duration by selectively inhibiting Kv1.5 could present safer pharmacological interventions for protecting against atrial re-entrant arrhythmias such as atrial fibrillation and atrial flutter compared to traditional class III antiarrythmics, by prolonging the atrial refractory period while leaving ventricular refractoriness unaltered (Nattel et al., 1999, Knobloch et al., 2002; and Wirth et al., 2003). Class III antiarrythmics have been widely reported as a preferred method for treating cardiac arrhythmias (Colatsky et al., 1990).
Drugs that maintain the sinus rhythm long-term without proarrhythmic or other side effects are highly desirable and not currently available. Traditional and novel class III antiarrythmic potassium channel blockers have been reported to have a mechanism of action by directly modulating Kv1.5 or Kv(ur). The known class III antiarrythmics ambasilide (Feng et al., 1997), quinidine (Wang et al., 1995), clofilium (Malayev et al., 1995) and bertosamil (Godreau et al., 2002) have all been reported as potassium channel blockers of Kv(ur) in human atrial myocytes. The novel benzopyran derivative, NIP-142, blocks Kv1.5 channels, prolongs the atrial refractory period and terminates atrial fibrillation and flutter in in vivo canine models (Matsuda et al., 2001), and S9947 inhibited Kv1.5 stably expressed in both Xenopus oocytes and Chinese hamster ovary (CHO) cells and Kv(ur) in native rat and human cardiac myocytes (Bachmann et al., 2001). Elsewhere, other novel potassium channel modulators which target Kv1.5 or Kv(ur) have been described for the treatment of cardiac arrhythmias, these include biphenyls (Peukert et al 2003), thiophene carboxylic acid amides (WO0248131), bisaryl derivatives (WO0244137, WO0246162), carbonamide derivatives (WO0100573, WO0125189) anthranillic acid amides (WO2002100825, WO02088073, WO02087568), dihydropyrimidines (WO0140231), cycloalkylamine derivatives (WO2005018635), isoquionolines (WO2005030791), quinolines (WO2005030792), imidazopyrazines (WO205034837), benzopyranols (WO2005037780), isoquinolinones (WO2005046578), cycloakyl derivatives (WO03063797), indane derivatives (WO0146155 WO9804521), tetralin benzocycloheptane derivatives (WO9937607), thiazolidone and metathiazanone derivatives (WO9962891), benzamide derivatives (WO0025774), isoquinoline derivatives (WO0224655), pyridazinone derivatives (WO9818475 WO9818476), chroman derivatives (WO9804542), benzopyran derivatives (WO0121610, WO03000675, WO0121609, WO0125224, WO02064581), benzoxazine derivatives (WO0012492), and the novel compound A1998 purified from Ocean material (Xu & Xu, 2000).
Compounds that are undergoing development for atrial fibrillation have recently been reviewed (Page and Rodin, 2005).
Furthermore, the related Kv1.3 channel is expressed in both white and brown adipose tissue, and skeletal muscle (Xu et al., 2004). Inhibition of the channel potentiates the hypoglycemic action of insulin, through increased insulin-stimulated glucose uptake in these tissues. This is supported by in vivo data, showing that Kv1.3 inhibition in mice with type-2 diabetes mellitus were significantly more sensitive to insulin. There is strong evidence that Kv1.3 inhibition improves peripheral glucose metabolism by facilitating GLUT4 translocation to the plasma membrane of adipocytes and myocytes (Desir, 2005). Small molecule inhibitors of Kv1.3 are emerging as potential targets in the management of type-2 diabetes, through their actions as insulin sensitisers (WO02-100248).
Human T-lymphocytes possess two types of potassium channels: the voltage-gated potassium Kv1.3 and the Ca2+-activated IKCa1 K+ channels (Leonard et al., 1992, Wulff et al., 2003a). These channels set the resting membrane potential of T-lymphocytes, playing a crucial role in the Ca2+ signal transduction pathways that lead to activation of these cells following antigenic stimulation. Disruption of these pathways can attenuate or prevent the response of T-cells to antigenic challenge resulting in immune suppression (Wulff et al., 2004).
The voltage-gated Kv1.3 and the Ca2+-activated IKCa1 K+ channels are expressed in T-cells in distinct patterns that accompany the proliferation, maturation and differentiation of these cells. The immunomodulatory effects of channel blockers depends on the expression levels of Kv1.3 and IKCa1 channels, which change dramatically when T-cells transition from resting to activated cells, and during differentiation from the naïve to the memory state. Kv1.3 channels dominate functionally in quiescent cells of all T-cell subtypes (naïve, TCM and TEM). Activation has diametrically opposite effects on channel expression; as naïve and TCM cells move from resting to proliferating blast cells, they upregulate IKCa1 channels. Consequently activated naïve and TCM cells express ˜500 IKCa1 channels and an approximately equivalent number of Kv1.3 channels. In contrast, activation of TEM cells enhances Kv1.3 expression without any change in IKCa1 levels. Functional Kv1.3 expression increases dramatically to 1500 Kv1.3 channels/cell, and their proliferation is sensitive to Kv1.3 blockers (Wulff et al., 2003, Beeton et al., 2003). B-cells also show a switch in K+ channel during differentiation that parallels the changes seen in the T-cell lineage (Wulff et al., 2004). The discovery that the majority of myelin-reactive T-cells in patents with MS are Kv1.3high TEM cells, has raised interest in the therapeutic potential of Kv1.3 blockers in autoimmune disorders (Wulff et al., 2003b, O'Connor et al., 2001). Kv1.3 blockers have been shown to ameliorate adoptive EAE induced by myelin-specific memory T cells (a model for MS) (Beeton et al., 2001) and to prevent inflammatory bone resorption in experimental periodontal disease caused mainly by memory cells (Valverde et al., 2005). In addition, there is increasing evidence implicating late memory cells in the pathogenesis of type-1 diabetes, rheumatoid arthritis, psoriasis, inflammatory bowel disorder, Crohn's disease, chronic graft rejection and chronic graft-vs-host disease (Frierich et al., 2000, Yoon et al., 2001, Viglietta et al., 2002, Yamashita et al., 2004). Specific Kv1.3 blockers might therefore constitute a new class of memory-specific immunomodulators (Shah et al., 2003).
Numerous novel small molecule Kv1.3 channel blockers have been reported for the management of autoimmune disorders. These include the iminodihydroquinolines WIN173173 and CP339818 (Nguyen et al., 1996), the benzhydryl piperidine UK-78,282 (Hanson et al. 1999), correolide (Felix et al., 1999), cyclohexyl-substituted benzamide PAC (U.S. Pat. No. 0,619,4458, WO0025774), sulfamidebenzamidoindane (U.S. Pat. No. 0,608,3986), Khellinone (Baell et al., 2004), dichloropenylpyrazolopyrimidine (WO-00140231) and psoralens (Wulff et al., 1998, Vennekamp et al., 2004, Schmitz et al., 2005).
Thienopyridines have been reported to be useful as antifungal agents, ligand-gated ion-channel modulators, antibacterials and enzyme inhibitors amongst others.
Thienopyridines substituted at the 2- and 3-positions by hydrogen, alkyl, cycloalkyl or aryl groups, at the 4-position by a hydroxyl group, at the 5-position by a carboxy group and by alkyl or aryl substitutents at the nitrogen of the 1-position have been claimed as potent antibacterial agents structurally related to the nalidixic acids (Gilis et al., 1978).
Thienopyridines substituted at the 3-position by a phenyl group, the 2-position by a methyl ketone, the 6-position by a phenyl group, the 5-position by a nitrile group or ester and at the 4-position by an amino group have been claimed as showing antifungal activity against fungi of the family Aspergillus and to inhibit mycotoxin production (Abdelrazek et al., 1992).
Thienopyridines substituted at the 2-, 3- and 6-positions by alkyl or aryl groups, at the 5-position by an ester, aldehyde or 3,5-dihydroxy heptenoic acid derivative and at the 4-position by a substituted phenyl group have been claimed as potent inhibitors of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) Reductase in vitro and to show marked cholesterol biosynthesis inhibitory activities in vivo (Suzuki et al., 2001).
Thienopyridines with a fused cycloalkyl ring between the 5- and 6-positions, and a phenyl group at the 2- and 3-positions have been shown to possess poor inhibitory activity against human acetylcholine esterase (Marco et al., 2002).
Thienopyridines have been claimed as anticancer agents with inhibitory action against the VEGF-2 receptor tyrosine kinase. Claimed compounds include those thienopyridines substituted at the 2-position with alkyl or aromatic moieties, unsubstituted at the 3-position and substituted at the 4-position by an amino group which may be secondary or tertiary and may be directly bound to an aromatic or heterocyclic moiety such as phenyl, indole or benzothiazole (U.S. Pat. No. 6,492,383 B1, Munchof et al., 2004).
Thieno[2,3-b]pyridines with a substituted aniline at the 4-position and a substituted phenyl group at the 2-position have been shown to have modest activity against the Src family of receptor tyrosine kinases as potential anticancer agents. (Boschelli et al, 2004).
Thieno[2,3-b]pyridines with an amino aryl or amino alkyl substituent at the 4-position, an amino group at the 3-position and a carbamoyl substituent at the 2-position have been claimed as modulators of HIV particle formation and Rev-dependant HIV production. (WO2005076861).
Tricyclic 4-amino-5,6,7,8-tetrahydrothieno[2,3-b]quinoline derivatives have been claimed as agents for inhibiting acetylcholinesterase and blocking K+ channels, which is claimed to be useful for activating lowered nerve function induced by senile dementia. (JP04134083).
Thienopyridines with a carbonyl group at the 2-position and an aryl group at the 3-position have been reported as being useful in the treatment of osteoporosis (JP07076586).
4-Amino-7-hydroxy-2-methyl-5,6,7,8-tetrahydrobenzo[b]thieno[2,3-b]pyridine-3-carboxylic acid, but-2-ynyl ester (SB205384) and other tricyclic analogues has been shown to modify the GABA-A receptor modulated chloride current in rat cerebellar granule cells (Meadows et al, 1997).